Combining a Fusion Inhibitory Peptide Targeting the MERS-CoV S2 Protein HR1 Domain and a Neutralizing Antibody Specific for the S1 Protein Receptor-Binding Domain (RBD) Showed Potent Synergism against Pseudotyped MERS-CoV with or without Mutations in RBD

Optimizing SARS-CoV-2 Immunoassays for Specificity in Dengue-Co-Endemic Areas

Introduction The overlap in clinical presentation between COVID-19 and dengue poses challenges for diagnosis in co-endemic regions. Furthermore, there have been reports of antibody cross-reactivity between SARS-CoV-2 and dengue. Our research aims to evaluate SARS-CoV-2 antigens for serological testing while reducing the possibility of cross-reactivity with anti-dengue antibodies. Method Two hundred and ten serum samples were collected from 179 patients and divided into four panels. Panels 1 and 2 consisted of COVID-19-negative healthy donors (n=81) and pre-pandemic dengue patients (n=50), respectively. Alternatively, Panel 3 (n=19) was composed of reverse transcription-quantitative polymerase chain reaction (RT-qPCR)-positive samples collected within two weeks of COVID-19 symptom onset, while Panel 4 (n=60) was composed of positive samples collected after two weeks of symptom onset. Previously developed and characterized in-house SARS-CoV-2 spike-1 (S1), receptor binding domain (RBD), and nucleocapsid (N) immunoglobin G (IgG)-enzyme-linked immunosorbent assay (ELISA) assays were used for the study. Results Six dengue-positive sera cross-reacted with the RBD of SARS-CoV-2. However, only one dengue-positive sera cross-reacted with the S1 and N proteins of SARS-CoV-2. Co-immobilization of S1 and RBD in different ratios revealed an 80:20 (S1:RBD) ratio as optimal for achieving an overall 96.2% sensitivity with the least cross-reaction to anti-dengue antibodies. Conclusion Our findings indicated that SARS-CoV-2 RBD-based immunoassays present more cross-reactivity with anti-dengue antibodies than S1 and N proteins. Furthermore, co-immobilization of S1 and RBD reduces the cross-reactivity with anti-dengue antibodies compared to RBD, thereby increasing the immunoassay specificity without affecting overall sensitivity for the dengue-endemic areas.

Pan-coronavirus fusion inhibitors to combat COVID-19 and other emerging coronavirus infectious diseases

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of the currently ongoing coronavirus disease 2019 (COVID-19) pandemic, has posed a serious threat to global public health. Recently, several SARS-CoV-2 variants of concern (VOCs) have emerged and caused numerous cases of reinfection in convalescent COVID-19 patients, as well as breakthrough infections in vaccinated individuals. This calls for the development of broad-spectrum antiviral drugs to combat SARS-CoV-2 and its VOCs. Pan-coronavirus fusion inhibitors, targeting the conserved heptad repeat 1 (HR1) in spike protein S2 subunit, can broadly and potently inhibit infection of SARS-CoV-2 and its variants, as well as other human coronaviruses. In this review, we summarized the most recent development of pan-coronavirus fusion inhibitors, such as EK1, EK1C4, and EKL1C, and highlighted their potential application in combating current COVID-19 infection and reinfection, as well as future emerging coronavirus infectious diseases.

Utilization of Recombinant Baculovirus Expression System to Produce the RBD Domain of SARS-CoV-2 Spike Protein

Continuous outbreaks of viral diseases in humans facilitates a need for the rapid development of viral test kits and vaccines. These require expression systems to produce a pure and high yield of target viral proteins. We utilized a baculovirus-silkworm expression system to produce the receptor binding domain (RBD) of the SARS-CoV-2 spike protein. First, we had to develop a strategy for constructing a recombinant baculovirus for RBD expression. For this, the coding region of the Bombyx mori cypovirus (BmCPV) polyhedron was assembled with the Bombyx mori nuclear polyhedrosis virus (BmNPV) promoter. We demonstrated that the recombinant baculovirus has the ability to form polyhedrons within host silkworm cells. In addition, the encapsulated BVs are able to infect silkworms by ingestion and induce foreign protein expression. In this way, we utilized this novel system to obtain a high yield of the target foreign protein, the RBD of the SARS-CoV-2 S protein. However, the viral infection rate of our recombinant BV needs to be improved. Our study shed light on developing a highly efficient expression system for the production of antigens and subsequent immunoassays and vaccines.

The Analogs of Furanyl Methylidene Rhodanine Exhibit Broad-Spectrum Inhibitory and Inactivating Activities against Enveloped Viruses, including SARS-CoV-2 and Its Variants

In recent years, infectious diseases caused by viral infections have seriously endangered human health, especially COVID-19, caused by SARS-CoV-2, which continues to spread worldwide. The development of broad-spectrum antiviral inhibitors is urgently needed. Here, we report a series of small-molecule compounds that proved effective against human coronaviruses (HCoV), such as SARS-CoV-2 and its variants of concern (VOCs), including Alpha (B.1.1.7), Beta (B.1.351), Gamma (P.1), Delta (B.1.617.2), and Omicron (B.1.1.529), SARS-CoV, MERS-CoV, HCoV-OC43, and other viruses with class I viral fusion proteins, such as influenza virus, Ebola virus (EBOV), Nipah virus (NiV), and Lassa fever virus (LASV). They are also effective against class II enveloped viruses represented by ZIKV and class III enveloped viruses represented by vesicular stomatitis virus (VSV). Further studies have shown that these compounds may exert antiviral effects through a variety of mechanisms, including inhibiting the formation of the six-helix bundle, which is a typical feature of enveloped virus fusion with cell membranes, and/or targeting viral membrane to inactivate cell-free virions. These compounds are expected to become drug candidates against SARS-CoV-2 and other enveloped viruses.

SARS-CoV-2 spike protein: Site-specific breakpoints for the development of COVID-19 vaccines

SARS-CoV2 is a member of human coronaviruses and is the causative agent of the present pandemic COVID-19 virus. In order to control COVID-19, studies on viral structure and mechanism of infectivity and pathogenicity are sorely needed. The spike (S) protein is comprised of S1 & S2 subunits. These spike protein subunits enable viral attachment by binding to the host cell via ACE-2 (angiotensin converting enzyme-2) receptor, thus facilitating the infection. During viral entry, one of the key steps is the cleavage of the S1-S2 spike protein subunits via surface TMPRSS2 (transmembrane protease serine 2) and results in viral infection. Hence, the S-protein is critical for the viral attachment and penetration into the host. The rapid advancement of our knowledge on the structural and functional aspects of the spike protein could lead to development of numerous candidate vaccines against SARS-CoV2. Here the authors discuss about the structure of spike protein and explore its related functions. Our aim is to provide a better understanding that may aid in fighting against CoVID-19 and its treatment.

Peptides derived from viral glycoprotein Gc Inhibit infection of severe fever with thrombocytopenia syndrome virus

Severe fever with thrombocytopenia syndrome (SFTS) is an acute infectious disease caused by a novel phlebovirus (SFTSV), characterized by fever, thrombocytopenia and leukocytopenia which lead to multiple organ failure with high mortality in severe cases. The SFTSV has spread rapidly in recent years and posed a serious threat to public health in endemic areas. However, specific antiviral therapeutics for SFTSV infection are rare. In this study, we demonstrated that two peptides, SGc1 and SGc8, derived from a hydrophobic region of the SFTSV glycoprotein Gc, could potently inhibit SFTSV replication in a dose-dependent manner without apparent cytotoxicity in various cell lines and with low immunogenicity and good stability. The IC₅₀ (50% inhibition concentration) values for both peptides to inhibit 2 MOI of SFTSV infection were below 10 μM in L02, Vero and BHK21 cells. Mechanistically, SGc1 and SGc8 mainly inhibited viral entry at the early stage of the viral infection. Inhibition of SFTSV replication was specific by both peptides because no inhibitory effect was shown against other viruses including Zika virus and Enterovirus A71. Taken together, our results suggested that viral glycoprotein-derived SGc1 and SGc8 peptides have antiviral potential and warrant further assessment as an SFTSV-specific therapeutic.

Emerging Technologies for the Treatment of COVID-19

The new coronavirus, named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), turned into a pandemic affecting more than 200 countries. Due to the high rate of transmission and mortality, finding specific and effective treatment options for this infection is currently of urgent importance. Emerging technologies have created a promising platform for developing novel treatment options for various viral diseases such as the SARS-CoV-2 virus. Here, we have described potential novel therapeutic options based on the structure and pathophysiological mechanism of the SARS-CoV-2 virus, as well as the results of previous studies on similar viruses such as SARS and MERS. Many of these approaches can be used for controlling viral infection by reducing the viral damage or by increasing the potency of the host response. Owing to their high sensitivity, specificity, and reproducibility, siRNAs, aptamers, nanobodies, neutralizing antibodies, and different types of peptides can be used for interference with viral replication or for blocking internalization. Receptor agonists and interferon-inducing agents are also potential options to balance and enhance the innate immune response against SARS-CoV-2. Solid evidence on the efficacy and safety of such novel technologies is yet to be established although many well-designed clinical trials are underway to address these issues.

Drug targets for COVID-19 therapeutics: Ongoing global efforts

The current global pandemic COVID-19 caused by the SARS-CoV-2 virus has already inflicted insurmountable damage both to the human lives and global economy. There is an immediate need for identification of effective drugs to contain the disastrous virus outbreak. Global efforts are already underway at a war footing to identify the best drug combination to address the disease. In this review, an attempt has been made to understand the SARS-CoV-2 life cycle, and based on this information potential druggable targets against SARS-CoV-2 are summarized. Also, the strategies for ongoing and future drug discovery against the SARS-CoV-2 virus are outlined. Given the urgency to find a definitive cure, ongoing drug repurposing efforts being carried out by various organizations are also described. The unprecedented crisis requires extraordinary efforts from the scientific community to effectively address the issue and prevent further loss of human lives and health.

Characteristics and serological patterns of COVID-19 convalescent plasma donors: optimal donors and timing of donation

BACKGROUND

The lack of effective treatments against the 2019 coronavirus disease (COVID‐19) has led to the exploratory use of convalescent plasma for treating COVID‐19. Case reports and case series have shown encouraging results. This study investigated SARS‐CoV‐2 antibodies and epidemiological characteristics in convalescent plasma donors, to identify criteria for donor selection.

METHODS

Recovered COVID‐19 patients, aged 18‐55 years, who had experienced no symptoms for more than 2 weeks, were recruited. Donor characteristics such as disease presentations were collected and SARS‐CoV‐2 N‐specific IgM, IgG, and S‐RBD‐specific IgG levels were measured by enzyme‐linked immunosorbent assay (ELISA).

RESULTS

Whereas levels of N‐specific IgM antibody declined after recovery, S‐RBD‐specific and N‐specific IgG antibodies increased after 4 weeks from the onset of symptoms, with no significant correlation to age, sex, or ABO blood type. Donors with the disease presentation of fever exceeding 38.5°C or lasting longer than 3 days exhibited higher levels of S‐RBD‐specific IgG antibodies at the time of donation. Of the 49 convalescent plasma donors, 90% had an S‐RBD‐specific IgG titer of ≥1:160 and 78% had a titer of ≥1:640 at the time of plasma donation. Of the 30 convalescent plasma donors, who had donated plasma later than 28 days after the onset of symptoms and had a disease presentation of fever lasting longer than 3 days or a body temperature exceeding 38.5°C, 100% had an S‐RBD‐specific IgG titer of ≥1:160 and 93% had a titer of ≥1:640.

CONCLUSION

This study indicates that the S‐RBD‐specific IgG antibody reaches higher levels after 4 weeks from the onset of COVID‐19 symptoms. We recommend the following selection criteria for optimal donation of COVID‐19 convalescent plasma: 28 days after the onset of symptoms and with a disease presentation of fever lasting longer than 3 days or a body temperature exceeding 38.5°C. Selection based on these criteria can ensure a high likelihood of achieving sufficiently high S‐RBD‐specific IgG titers.

Coronavirus membrane fusion mechanism offers a potential target for antiviral development

The coronavirus disease 2019 (COVID-19) pandemic has focused attention on the need to develop effective therapies against the causative agent, SARS-CoV-2, and also against other pathogenic coronaviruses (CoV) that have emerged in the past or might appear in future. Researchers are therefore focusing on steps in the CoV replication cycle that may be vulnerable to inhibition by broad-spectrum or specific antiviral agents. The conserved nature of the fusion domain and mechanism across the CoV family make it a valuable target to elucidate and develop pan-CoV therapeutics. In this article, we review the role of the CoV spike protein in mediating fusion of the viral and host cell membranes, summarizing the results of research on SARS-CoV, MERS-CoV, and recent peer-reviewed studies of SARS-CoV-2, and suggest that the fusion mechanism be investigated as a potential antiviral target. We also provide a supplemental file containing background information on the biology, epidemiology, and clinical features of all human-infecting coronaviruses, along with a phylogenetic tree of these coronaviruses.

Coronavirus membrane fusion mechanism offers a potential target for antiviral development

The coronavirus disease 2019 (COVID-19) pandemic has focused attention on the need to develop effective therapies against the causative agent, SARS-CoV-2, and also against other pathogenic coronaviruses (CoV) that have emerged in the past or might appear in future. Researchers are therefore focusing on steps in the CoV replication cycle that may be vulnerable to inhibition by broad-spectrum or specific antiviral agents. The conserved nature of the fusion domain and mechanism across the CoV family make it a valuable target to elucidate and develop pan-CoV therapeutics. In this article, we review the role of the CoV spike protein in mediating fusion of the viral and host cell membranes, summarizing the results of research on SARS-CoV, MERS-CoV, and recent peer-reviewed studies of SARS-CoV-2, and suggest that the fusion mechanism be investigated as a potential antiviral target. We also provide a supplemental file containing background information on the biology, epidemiology, and clinical features of all human-infecting coronaviruses, along with a phylogenetic tree of these coronaviruses.

Engineering a Novel Antibody-Peptide Bispecific Fusion Protein Against MERS-CoV

In recent years, tremendous efforts have been made in the engineering of bispecific or multi-specific antibody-based therapeutics by combining two or more functional antigen-recognizing elements into a single construct. However, to the best of our knowledge there has been no reported cases of effective antiviral antibody-peptide bispecific fusion proteins. We previously developed potent fully human monoclonal antibodies and inhibitory peptides against Middle East Respiratory Syndrome Coronavirus (MERS-CoV), a novel coronavirus that causes severe acute respiratory illness with high mortality. Here, we describe the generation of antibody-peptide bispecific fusion proteins, each of which contains an anti-MERS-CoV single-chain antibody m336 (or normal human IgG1 CH3 domain as a control) linked with, or without, a MERS-CoV fusion inhibitory peptide HR2P. We found that one of these fusion proteins, designated as m336 diabody-pep, exhibited more potent inhibitory activity than the antibody or the peptide alone against pseudotyped MERS-CoV infection and MERS-CoV S protein-mediated cell-cell fusion, suggesting its potential to be developed as an effective bispecific immunotherapeutic for clinical use.

Identification of Novel Natural Products as Effective and Broad-Spectrum Anti-Zika Virus Inhibitors

Zika virus (ZIKV) infection during pregnancy leads to severe congenital Zika syndrome, which includes microcephaly and other neurological malformations. No therapeutic agents have, so far, been approved for the treatment of ZIKV infection in humans; as such, there is a need for a continuous effort to develop effective and safe antiviral drugs to treat ZIKV-caused diseases. After screening a natural product library, we have herein identified four natural products with anti-ZIKV activity in Vero E6 cells, including gossypol, curcumin, digitonin, and conessine. Except for curcumin, the other three natural products have not been reported before to have anti-ZIKV activity. Among them, gossypol exhibited the strongest inhibitory activity against almost all 10 ZIKV strains tested, including six recent epidemic human strains. The mechanistic study indicated that gossypol could neutralize ZIKV infection by targeting the envelope protein domain III (EDIII) of ZIKV. In contrast, the other natural products inhibited ZIKV infection by targeting the host cell or cell-associated entry and replication stages of ZIKV. A combination of gossypol with any of the three natural products identified in this study, as well as with bortezomib, a previously reported anti-ZIKV compound, exhibited significant combinatorial inhibitory effects against three ZIKV human strains tested. Importantly, gossypol also demonstrated marked potency against all four serotypes of dengue virus (DENV) human strains in vitro. Taken together, this study indicates the potential for further development of these natural products, particularly gossypol, as the lead compound or broad-spectrum inhibitors against ZIKV and other flaviviruses, such as DENV.

Antibodies and vaccines against Middle East respiratory syndrome coronavirus

The Middle East respiratory syndrome coronavirus (MERS-CoV) has spread through 27 countries and infected more than 2,200 people since its first outbreak in Saudi Arabia in 2012. The high fatality rate (35.4%) of this novel coronavirus and its persistent wide spread infectiousness in animal reservoirs have generated tremendous global public health concern. However, no licensed therapeutic agents or vaccines against MERS-CoV are currently available and only a limited few have entered clinical trials. Among all the potential targets of MERS-CoV, the spike glycoprotein (S) has been the most well-studied due to its critical role in mediating viral entry and in inducing a protective antibody response in infected individuals. The most notable studies include the recent discoveries of monoclonal antibodies and development of candidate vaccines against the S glycoprotein. Structural characterization of MERS-CoV S protein bound with these monoclonal antibodies has provided insights into the mechanisms of humoral immune responses against MERS-CoV infection. The current review aims to highlight these developments and discuss possible hurdles and strategies to translate these discoveries into ultimate medical interventions against MERS-CoV infection.

Recent Aspects on the Pathogenesis Mechanism, Animal Models and Novel Therapeutic Interventions for Middle East Respiratory Syndrome Coronavirus Infections

Middle East Respiratory Syndrome Coronavirus (MERS-CoV) is an emerging zoonotic virus considered as one of the major public threat with a total number of 2 298 laboratory-confirmed cases and 811 associated deaths reported by World Health Organization as of January 2019. The transmission of the virus was expected to be from the camels found in Middle Eastern countries via the animal and human interaction. The genome structure provided information about the pathogenicity and associated virulent factors present in the virus. Recent studies suggested that there were limited insight available on the development of novel therapeutic strategies to induce immunity against the virus. The severities of MERS-CoV infection highlight the necessity of effective approaches for the development of various therapeutic remedies. Thus, the present review comprehensively and critically illustrates the recent aspects on the epidemiology of the virus, the structural and functional features of the viral genome, viral entry and transmission, major mechanisms of pathogenesis and associated virulent factors, current animal models, detection methods and novel strategies for the development of vaccines against MERS-CoV. The review further illustrates the molecular and computational virtual screening platforms which provide insights for the identification of putative drug targets and novel lead molecules toward the development of therapeutic remedies.

Advances in MERS-CoV Vaccines and Therapeutics Based on the Receptor-Binding Domain

Middle East respiratory syndrome (MERS) coronavirus (MERS-CoV) is an infectious virus that was first reported in 2012. The MERS-CoV genome encodes four major structural proteins, among which the spike (S) protein has a key role in viral infection and pathogenesis. The receptor-binding domain (RBD) of the S protein contains a critical neutralizing domain and is an important target for development of MERS vaccines and therapeutics. In this review, we describe the relevant features of the MERS-CoV S-protein RBD, summarize recent advances in the development of MERS-CoV RBD-based vaccines and therapeutic antibodies, and illustrate potential challenges and strategies to further improve their efficacy.